Towards Wearability in Fingertip Haptics: A 3-DoF Wearable Device for Cutaneous Force Feedback

Teleoperated minimally invasive surgical robots can significantly enhance a surgeon's accuracy, dexterity and visualization. However, current commercially available systems do not include significant haptic (force and tactile) feedback to the operator. This paper describes experiments to characterize this problem, as well as several methods to provide haptic feedback in order to improve surgeon's performance. There exist a variety of sensing and control methods that enable haptic feedback, although a number of practical considerations, e.g. cost, complexity and biocompatibility, present significant challenges. The ability of teleoperated robot-assisted surgical systems to measure and display haptic information leads to a number of additional exciting clinical and scientific opportunities, such as active operator assistance through "virtual fixtures" and the automatic acquisition of tissue properties.

Small patches of fingerpad glabrous skin in human subjects were tested in vivo for their biomechanical properties under tangential loading and for large deformations. These conditions included stretching and shearing the skin at a length scale of 0.3mm using an apparatus comprising a pair of piezoelectric benders arranged to increase the stiffness/free deflection tradeoff when compared to ordinary cantilevered benders. It was then possible to test the skin with up to 80% of tangential strain. With feedback control, it was also possible to create isotonic and isometric testing conditions. The results showed much variability across subjects and it was seen that the glabrous skin exhibited nonlinear stiffening in tangential traction. The skin was consistently more elastic across the ridges than along the ridges regardless of the location of the sample on the fingerpad. The skin behaved visco-elastically but relaxed about twice as fast than it crept. Finally, it was found that under large deformation, there was consistently 80% of hysteretic loss for a wide range of loading conditions.